Dive Bombers — A Brief History of the First Precision Strike Aircraft

The Ju-87 Stuka was Germany’s front-line dive bomber at the outbreak of the Second World War. Interestingly, both Japan and the United States would field their own version of the aircraft. All three powers would use dive bombers with devastating effect in the conflict. (Image source: WikiMedia Commons)

“Each airplane enabled their respective services to perfect dive-bombing as a tactic. Each introduced new (at the time) technology and solutions that made them accurate dive bombers.”

By Marc Liebman

IN THE AGE of smart glide bombs and missiles, air forces and navies still practice delivering old-fashioned “dumb” bombs in a steep dive, much like they did during the Second World War. Why is this? Because dive bombing remains the most accurate way to hit a moving or stationary target with an unguided bomb.

The history of dive bombing is a long one that stretches back more than 100 years. The earliest successful dive bomb raid occurred on October 8, 1914, when a pilot with the Royal Navy Air Service (the forerunner to the Fleet Air Arm) flying from an airfield at Antwerp bombed a Zeppelin shed at Dusseldorf, Germany. The flier, future air vice marshal Reginald Marix, struck the target by diving steeply from more than 3,000 feet and releasing a bomb at 600 feet. The attack destroyed the hangar and the airship LZ-25 and won Marix the Distinguished Service Order and a promotion.

As the war progressed, the Royal Flying Corps (later the Royal Air Force) and the United States Army Air Service ordered their pilots to dive at trenches, open fire with their machine guns and drop small bombs from low altitude – three or four hundred feet – on the Germans below. Pull-out was at about 100 feet. While both the pilots and the soldiers in the trenches saw the effectiveness of the technique, the airplanes and fliers were very vulnerable to ground fire. Not surprisingly, many planes were damaged or lost in these dive-bombing runs.

After the Great War, the RAF sought to improve the practice of dive-bombing through trials using Sopwith Camels and S.E.5as. The British soon concluded that it was “quite unsafe for the average pilot to dive at the target and the results expected are not worth the expenditure of machines and trained pilots.”

After conducting similar trials, the U.S. Army Air Service, later the U.S. Army Air Corps, reached similar conclusions to the RAF’s: dive bombing was simply too dangerous to be practical.

A glide bomb attack. (Image source: The author)

A dive bomb attack. (Image source: The author)

After all, dive bombing is an inherently dangerous maneuver. Unlike glide bombing, an at-best moderately accurate technique in which a pilot dips the nose 30 degrees and releases a bomb that follows a trajectory towards the target, dive bombing allows for more precision attacks, albeit with much greater risk.

In this form of attack, the pilot rolls the airplane into a steep turn abeam of the target and pushes the nose almost straight down, so it is 70 to 80 degrees below the horizon. When the bomb is released, it follows the trajectory of the airplane, after which the pilot pulls back on the stick, retracts the dive brakes and makes a three to four G (or more) pull out.

Dive bombing was indeed challenging. The stress of it was hard on both pilots and aircraft.

Interestingly enough, the U.S. Navy and U.S. Marine Corps had different thoughts. Many in those branches believed that dive-bombing, despite the risks, had a role in future warfare.

In the 1920s, the Marines fighting in Nicaragua used dive-bombers effectively in close air support roles. Meanwhile, the U.S. Navy thought it was an ideal way to sink enemy ships, if the tactics could be perfected and an aircraft that could be controlled in a steep dive could somehow be developed.

The U.S. Navy was not alone in its faith in dive bombing. Both the Imperial Japanese Navy and the emerging German Luftwaffe saw dive-bombing the same way the U.S. Navy and Marine Corps did.

By the 1930s, all of these militaries were experimenting with various designs, albeit with limited success.

The Curtiss F8C-4 Falcon entered service with the U.S. Army and Navy in the late 1920s as a fighter-bomber. The Marines used the aircraft as a dive-bomber, which it christened the Helldiver. It would be the first of three different Curtiss warplanes to bear that name. (Image source: WikiMedia Commons)

The early biplane dive-bombers, such as the American Curtiss F8C-4s, the German Heinkel He-50, and the Japanese Aichi D1A, were very “draggy.” That means when the pilots pointed the nose down to dive on a target, there was so much drag from the additional wing, the planes couldn’t accelerate much beyond 200 knots.

The introduction of the monoplane solved the issue of drag. Yet even that new game-changing design, without the second wing, or drag-causing supporting struts and wires, was not automatically suitable for dive bombing either. Indeed, the sleek lines and retractable landing gear on many newer model monoplanes made them too fast for dive bombing. In fact, pilots of dive bombers like the Vought SBU Vindicator needed to go into dives with their landing gear lowered to reduce speed. Even then, lowering the landing gear didn’t enable dives as deep as 70 to 80 degrees from the vertical. The British Blackburn Skua and early models of the Douglas SBD could also pick up too much speed on dives. What was needed were what we now know as dive brakes.

Designers had to put on their thinking caps because in the 1930s, the focus was on streamlining, i.e., reducing induced drag (drag caused by the airplane going through the air) and parasite drag (drag caused by the structure/design of the airplane). Dive brakes, aeronautical engineers found, caused a whole new set of problems such as turbulence that was violent enough to cause structural failure of the horizontal stabilizer or reduced the effectiveness of all three control surfaces. Dive brakes added weight and complexity to the airplane.

Herman Polhmann at Germany’s Junkers aircraft company and Ed Heinemann of Northrop and later Douglas came up with totally different solutions as did Japanese designers.

In fact, by the Second World War all three powers would introduce their own version of dive bombers featuring dive brakes. Japan produced the Aichi D3A1/2 “Val”; The U.S. Navy and Marines fielded the Douglas SBD 3/4/5 series; while Germany’s Junkers Ju-87B/D “Stuka” became a major component of Blitzkrieg. Each airplane enabled their respective services to perfect dive-bombing as a tactic. Each introduced new (at the time) technology and solutions that made them accurate dive bombers.

All three of these aircraft were in frontline service at the start of the Second World War. And while each would see their production ended in 1944, all were still in frontline service at the end of the war. The Val had been pulled back to training duties and was pressed into service as a kamikaze, while the Stuka, long since rendered obsolete, G variants were outfitted with tank-killing 37-mm guns and soldiered on as effective ground attack aircraft. And while the SBD was being replaced by the Curtiss SB2C-4s, Marine Corps units kept flying them on combat missions until the end of the war.

The Ju-87’s dive brakes were split flaps that spanned the entire wing. The flaps extended behind the trailing edge of the wing and, depending on the position selected by the pilot, were either dive brakes or provided more lift at slow speeds. (Image source: WikiMedia Commons)

The Stuka

The Junkers Ju-87 was the first of the three dive bombers to enter service. It was combat tested during the 1936 to 1939 Spanish Civil War by crews of the German Condor Legion.

The German solution to dive brakes were split flaps that ran the length of the winds. In a dive, the flaps were extended above and below the wing. For landing, only the lower half were extended, and there was a gap between the leading edge of the flaps and the trailing edge of the wing. This led to an airplane that was very controllable at low speeds.

The other major innovation of the Ju-87 was its dive recovery system. Before the pilot rolled into the dive, he set the bomb release altitude into the plane’s autopilot. Once he released the bombs, the autopilot would pull the stick back in a three to four-G pullout and retract the dive brakes.

Stukas, which is the short version of the German word for dive bomber — Sturkampfflugzeug — also had a window on the floor of the cockpit that the pilot could look through to keep his target in sight as he flew over it.

Although designed as a dive bomber, Ju-87s also carried torpedoes in an anti-shipping role, and several were built with folding wings for use on the planned German aircraft carrier, the Graf Zeppelin.

Dive brakes on the D3A2 Val were mounted under the wing and were extended (as seen here) during the dive. When deployed, the dive brakes were almost perpendicular to the wing and consisted of two strips of aluminum separated by a slot. Note the ‘gunsight’ extending forward from the cockpit. This helped the pilot aim the bombs in dives.

The Val

The fixed-gear Aichi D3A1 and 2 was a 1937 design that entered IJN service in 1939. Japanese engineers used dive brakes that were split panels that extended from the top and bottom of the wing. They were about one-quarter the span on each side. Pilots aimed their bombs by focusing on the crosshairs in the telescopic gunsight mounted ahead of the cockpit.

In addition, the radio operator/gunner had a drift sight and meter to help gauge the wind for dive and level bombing and a very accurate reflector compass to take bearings and help with navigation.

Unfortunately for the crew, the D3A1/2 was not equipped with any armor for the crew or self-sealing fuel tanks.

The primary difference between the D3A1 and D3A2 was the 1,300 Mitsubishi Kinsei 54 engine in the D3A2 replacing the 1,000 hp Kinsei 44 in the D3A1. Code named Val by the Allies, the D3A1/2 was maneuverable and at times, was pressed into service as a fighter.

Douglas SBD

The SBD is the only one of the three dive-bombers with retractable landing gear. It is the only one not built by the company that had the first design and production contract.

The plane began with a Northrop design by Ed Heinemann known as the BT1 and BT2. However, after the first Navy contract for the BT2 was issued, Northrop sold the contract, the design team and its factory in El Segundo, California to Douglas Aircraft.

When delivered, the BT2 had two major issues. One of which was poor directional control at slow speeds which made both airplanes tricky to land on a carrier. The other was buffeting of the tail when the dive flaps were extended.

Heineman designed a larger rudder with a dorsal fin to improve directional stability and installed perforated flaps that, when extended above and below the wing, kept the speed of the SBD down to about 240 knots in a 70- to 80-degree dive. They also worked well to reduce the landing speed.

Dive brake retraction in the SBD, as in the Val, was manual. In other words, once the pilot dropped his bombs, and began his pullout, he had to retract the flaps.

The SBD is the only one of the three airplanes to have a set of controls so that if the pilot was incapacitated, the radio-operator gunner could fly the airplane.

Early models of the SBD had a telescopic gunsight that often fogged up as the airplane descended from colder high altitudes to the hot, humid air over the Southwestern Pacific. The solution was to heat the sight, and later, it was replaced with a reflecting gun sight like the one used in the F4F Wildcat, the F6F Hellcat and the F4U Corsair.

The advent of rockets allowed any aircraft, whether it was a dive-bomber or not, to attack surface targets with greater precision than bombs. Although dive bombers would disappear as a type of warplane, the practice would continue. (U.S. Air Force photo)

The End of the Dive Bomber?

For much of the early years of the Second World War, dive bombers were remarkably effective.

In addition to being able to deposit a bomb with great precision, they were difficult to shoot down. The rapid rate of the plane’s descent complicated the firing solution for any anti-aircraft gunner defending the target. For a gunner firing a manually tracked gun, a descending dive bomber was very difficult to hit.

Intercepting fighters also had trouble stopping dive-bomber runs. Without dive brakes of their own, fighter pilots who tried to shoot down the bombers from the six o’clock position would speed past the enemy plane leaving themselves vulnerable to dive bomber’s forward-firing guns. The only other solutions were to either intercept the enemy planes before they pushed over into their dives. Failing that, the alternatives were a hard-to-execute deflection shot or to wait until the dive bomber released its bombs and then attack it as it resumed level flight.

A U.S. Navy F-4 Phantom II dives on a target in Vietnam.

Although supplanted by precision guided ordnance, dive bombing is still a technique that’s taught and practiced today.

Even though the speeds and release altitudes are different for modern warplanes, it remains the best and most accurate method to put “dumb” bombs on target.

What’s more, most modern jets — military and civilian — have descendants of the dive brakes that can trace their lineage back to these three airplanes. Every tactical military jet has a set of “speed brakes” that can drastically reduce its speed. Civilian airliners have slotted flaps à la the Ju-87 that extend aft of the trailing edge of the wing and “spoilers” that can be raised above the wing similar to the SBD and D3A to increase the rate of descent and to help slow the plane after touchdown.

Marc Liebman is a retired U.S. Navy Captain and Naval Aviator and the award-winning author of 14 novels, five of which were Amazon #1 Best Sellers. His latest is the counterterrorism thriller The Red Star of Death. Some of his best-known books are Big Mother 40, Forgotten, Moscow Airlift, Flight of the Pawnee, Insidious Dragon and Raider of the Scottish Coast. All are available on Amazon here.